Reamer attachments for earth drilling apparatus



March 28, 1967 J. A. MEREDITH 3,331,379

REAMER ATTACHMENTS FOR EARTH DRILLING APPARATUS Filed Jan. 6, 1964 5Sheets-$heet l INVENTOR, JOHN A. MEREDiTH A ORNEY March 28, 1967 J. A.MEREDITH 3,311,179

REAMER ATTACHMENTS FOR EARTH DRILLING APPARATUS Filed Jan. 6, 1964 5sheets-sheet 2 H L 1 I9 50 11 -& 49 8 2g 49 F/6 4 INVENTOR.

JOHN A. MEREDITH BY paw 7% A ORNEY March 28, 1967 J. A. MEREDITH3,311,179

REAMER ATTACHMENTS FOR EARTH DRILLING APPARATUS Filed Jan. 6, 1964 5Sheets-Sheet 5 INVENTOR.

JOHN A- MEREDITH ATTORNEY United States Patent The present inventionrelates to earth drilling apparatus and, more particularly, to equipmentand apparatus of the foregoing type that is well adapted for enlargingthe size and bore of drill holes.

In recent years powered equipment has been designed and built for thedrilling of caisson footings and the like. In addition to the provisionof powered apparatus for rotating the drill apparatus, furtherimprovements have been made in the design and construction of the boringtool itself. As the result of the combined advances in technology, it isnow possible and economically feasible to provide drilled caissonfootings for many different types of building construction. The caissonsas installed or cast in place in the earth holes provide secure andstable foundations for buildings of ever increasing size.

The success in the application of drilled footings to smaller structureshas indicated the desirability of adapting the same constructiontechniques to larger structures. This has required the provision ofheavier and larger equipment for drilling holes of ever increasingdiameter and of similarly increased depth. The resultant changes in thepower driving equipment and in its capability to drill holes of largerdiameter and deeper extent have made it possible through provision ofthe present apparatus to facilitate the installation of massivestructures of considerable military and defense importance.

The combination of the larger power driving equipment and theattachments described herein now makes it possible to drill holes inearth structures of sufficient diameter and depth to receiveintercontinental ballistic missile launch facilities. V/ith suchequipment all necessary earth work for the installation of suchfacilities can be accomplished expeditiously and economically.

Accordingly, while the general objective of the present invention hasbeen to provide attachments and equipment that will facilitate thedrilling of large caisson holes, a companion objective has been toprovide such equipment that would facilitate the installation of missilelaunching facilities with a consequent saving in time and money.

Specific objects of the present invention are the provision of earthauger attachments adapted to enlarge and ream previously drilled holesso that openings of larger diameter and depth may be provided withoutexceeding the torque and driving capabilities of conventional earthauger equipment.

A further object of the invention is the provision of reamer attachmentsspecifically adapted to ream and undercut an earth structure to providean enlarged footing or collar in spaced position along the verticalextent of the drilled hole.

Another object of the invention is to provide attach ments for earthauger driving apparatus which will facilitate the drilling of earthopenings peculiarly well adapted to the installation of missile launchfacilities.

Further and additional objects of the present invention will be apparentfrom the appended description and drawings, in which FIG. 1 is a topplan view in partial broken section showing construction details of anunder-reamer attachment made in accordance with the present invention,

FIG. 2 is a side elevation showing further features of the attachmentillustrated in FIG. 1,

ice

FIG. 3 is a top plan view illustrating the configuration of a reamerattachment for earth auger equipment,

FIG. 4 is a side elevation in partial section showing additional detailsin the construction of said reamer attachment,

FIG. 5 is a side sectional elevation illustrating progressive steps inthe digging of a missile launching facility,

FIG. 6 is a side elevation showing the under-reamer techniques used inconnection with such construction, and

FIG. 7 is a perspective view and diagram of said reamer attachment.

Briefly stated, the present invention provides reamer and under-reamerattachments for earth auger equipment so that the hole size capacity ofeven the largest present day earth drilling equipment may be extended.In general, separate embodiments of the invention are shown which arespecifically provided for the purpose of reaming a drilled opening to alarger size and, separately, for underreaming the sides of a previouslydrilled or reamed hole to provide a bell footing or collar for suchhole. The reamer attachment provides outrigger arms and supports for aplurality of cutters which are disposed to progressively engage thewalls of earth surrounding a previously drilled hole as necessary toenlarge the bore of such hole while accurately maintaining the locationof such hole. The under-reamer is provided with adjustable support meanswhereby the effective horizontal extension of the cutting apparatus maybe progressively changed to provide an under-reamed footing or collarfor a previously drilled and reamed opening.

Before explanation of the details of specific embodiments of theinvention, it is believed advisable to first disclose the nature of atypical cycle of operation. A representative step process is discerniblefrom a study of FIGURES 5 and 6. Here it will be seen that an earthstructure 11 has first been drilled with a conventional auger 16 toprovide a hole 12 which is of the largest diameter possible within thetorque and depth capacity of a drilling apparatus 14. The hole 12usually will be drilled through use of a conventional screw flight typeof auger 16 which is for descriptive purposes shown at the bottom ofhole 12 in FIGURE 5. Necessarily, such auger 16 will ordinarily beremoved from the hole by the retraction of the kelly bar 17 uponcompletion of the initial bore 12.

After completion of such initial bore 12, the reamer attachment 18, asmore fully illustrated in FIGURES 3 and 4, will be positioned on thekelly bar 17, and the size of the drilled opening will be enlarged firstby the lower cutters 19 and thereafter by the upper cutters 21 until theenlarged hole or opening 22 ha been obtained. Use of the reamerattachment will be continued until the buildup of loosened earthproducts in the lower hole 12 stops the further progress of suchoperations. Thereafter, the auger attachment 16 or other clean-outapparatus may again be placed on the equipment to clean out theaccumulated debris at the bottom of hole 12. The reamer attach-ment 18will thereafter be again placed on the kelly bar 17, and the reamingfunction will be continued. Actually, in some instances the dirthoisting and carrying capacity of the reamer 18 may itself 'be utilizedto raise the loosened earth out of the bottom of the hole.

By proper interchange of attachments the full depth of an enlar ed hole22 may be completed. Thereafter, operations may be continued with theunder-reamer attachment 23 shown diagrammatically in FIGURE 6 and indetail in FIGURES 1 and 2 so that the hole 22 may be provided with anenlarged hell or footing 24 and, if desired, a top or intermediatecollar portion 26. In the use of this under-reamer apparatus the cutterarms 27 and the associated cutter bits thereon will be retracted untilthe under-reamer 23 is at the bottom of the previously drilled hole 22.Thereafter, the arms 27 will be progressively extended until the desiredenlarged diameter has been attained. Subsequent rotation and raising ofthe under-reamer will then cut the desired bell footing 24 or collar 26.Upon removal of all of the loosened materials a finished opening oflarge diameter having top and bottom collars and footings of increasedsize and diameter will be obtained.

For the purpose of establishing relationships in size as necessary for afurther understanding of the nature and function of the apparatus to beherein described, it should be noted that the drilled holes 12 .maythrough use of present designs and equipment be on the order of ten feetin diameter and up to eighty-five feet deep. The reamer attachment 18can efiiciently enlarge the size of the hole 12 to provide an opening 22that is fourteen feet in diameter and of the described depth. Thepresently described under-reamer 23 can thereafter enlarge the derivedhole or opening 22 to provide collar and footing sections of sixteenfoot diameter.

The detailed features of preferred embodiments of the generallydescribed reamer and under-reamer apparatus are shown respectively inFIGURES 3, 4 and 7, and 1 and 2. The reamer attachment 18, as shown inFIGURES 3, 4 and 7, is a massive structure of rigid constructionproviding a strong frame 28 made up of a plurality of elements which, ingeneral, radiate from a central kelly socket 29 to deliver the torqueforces exerted by the kelly bar outwardly to the various cutterelements. Specifically, the kelly socket 29 is a vertically disposedhollow element of square cross-section adapted to receive the kelly bar17 or kelly bar extension of earth auger apparatus. In conventionalmanner a hole 31 is provided so that a pin may be placed through thekelly bar and socket 19 to hold the two element in assembled relation.

The general frame structure 28 of the reamer 18 extends radiallyoutwardly from the kelly bar socket 29 and includes the use of lowercross bars 33. These cross bars are preferably wide flange beams, and inthe apparatus previously described are of approximately 14 inch size.The lower cross bar 33 provide support for a circular guide ring 34which is provided with an outer tapered surface and which is preferablyof a size to engage and be guided by the sidewalls of a previouslydrilled hole, such as the illustrated hole 12 shown in FIGURE 5.

A guide ring 36 is disposed above guide ring 34 to likewise engage theslightly reamed sidewall of the hole so that the entire reamer 18 isprovided with an initial hole guiding contact which tends to prevent theentire reamer apparatus from deviating from the central bore of theoriginally provided hole 12.

As shown in FIGURES 4 and 7, the upper and lower guide rings 36 and 34provide support for connecting elements 37 disposed in quadrantpositions about the kelly socket 29. These connecting elements 37 aredisposed along the tapered contour defined by the upper and lower guiderings 36 and 34 and further provide support for cutter bit sockets 38and the associated cutter bits 39. These cutter bits 39 extend outwardlyfrom the sockets 38 to engage the earth walls as necessary to cut thetapered surface. In connection with the positioning of these cutter bits39, it should be noted that the sockets and bits are disposed at variouspositions along the substantially vertical extent of the supports 37 sothat the bits at one quadrant position are not at the same level a thosein a following quadrant position. Accordingly, each bit will cut adistinctive and separate path as the reamer 18 is rotated. The cutterbits 39 in position between the lower and upper guide rings 34 and 36cut a pilot bore in the earth structure having a regularly taperedsurface. The degree of outwardly disposed angle for such taper isrelatively limited so that an excessive cutting load will not be imposedon any specific cutter bit 39. With diminished cutting load a near trueand accurate pilot bore may be obtained.

After attainment of the desired pilot bore, a heavier cuttlng functionmay be carried out by successive extensions on the reamer apparatus 18with little danger of deviating from the true bore of the original hole12. Preferably the desired extension cuts are made in steppedarrangement to avoid excessive loadings on the reamer 18, the kelly bar17 and on the drive apparatus itself. FIGURES 3, 4 and 7 illustrate areamer attachment 1% in which at least two separate extensions areprovided. A first or intermediate extension 41 is disposed in radialposition intermediate the position for the second or top extension 42.Accordingly, as the apparatus is rotated the cutter bits 19 of theintermediate extension will be cutting at a position ninety degreesout-of-phase with respect to the cutter bits 21 of the top extension. Asin the previous instance, it should likewise be noted that the separatecutter bits 39 of the cutter group 19 are again in out-of-line positionwith respect to the corresponding cutter bits 19 in the diametricallyopposed group at the same intermediate extension level. This is the samedispersed cutter bit pattern as that utilized in connection with thepilot bore section and in the top extension.

The upwardly and outwardly directed angular position for the cutter bitson the intermediate and top extensions is similar but of considerablygreater degree than the taper angle for the pilot bore section. Becauseof the increased angle, the intermediate and top extensions account forthe major enlargement in the diameter of the drilled and reamed holes.Since the cutters for the intermediate extension, disposed atdiametrically opposed positions, are at a lesser radial distance thanthe top extension cutters, and since it is desirable to balance thecutting load about the circumference of the reamer attachment 18, theradial cutting width of the intermediate extension is slightly greaterthan that for the top extension which will be cutting earth at a greaterdistance away from the central kelly bar. Regulation of the number,placement and radial distance of the separate cutter bits on theintermediate and top extensions, respectively, can effectively balancethe torque loading on the reamer attachment 18 notwithstanding theninety degree relative positioning for said intermediate and topextensions.

The step arrangement of the intermediate and top extensions has beenfound preferable to a single tapered disposition for the cutter bits forseveral reasons. First the stepped arrangement makes it possible toprovide additional guide elements at both the point of departure and thepoint of finish for each individual taper. These guide elements help topreserve the desired direction of bore for the apparatus. The guideelements for the top and intermediate extensions may be of full circularextent, but the segmental arc elements 46 and 47, as shown, arepreferred.

In addition to the provision of improved guide functrons, the steppedarrangement for the tapered extensions provides a better result due tothe inherent nature of earth structures themselves. The stepped cuttingarrangement makes it easier for the cutter bits to break away largersegments of bedded earth structures, and, accordmgly, the cutting actionproceeds at a faster pace.

The actual placement and bracing of the intermediate and top extensionsutilizes main supports 48 and 49 joined to the kelly socket 29 and intoother frame or frame support members, such as the guide elements 46 and47. Cross braces 50 are also used to support the elements 46 and 47 inthe desired circular arrangement.

Since it is often necessary for attendant personnel to be lowered intothe hole as the digging proceeds, a deck plate 52 may be provided aboveand across the lower cross bars 33. This provides a platform when itbecomes necessary to change the cutter bits or when inspection atthebottom of the hole is required for other purposes.

While the use of intermediate and top extensions has been shown, it istrue that where the required enlargement of the hole is not of therelative proportion described, a single extension level could be used.Necessarily, the cutting load disposed on opposite sides of the pilotbore should be equalized, and, accordingly, a balanced arrangement ofextension elements should be used. A balanced arrangement will assureproper alignment of the bore and will also make it possible to maintainsomewhat equal torque forces with respect to the central location of thekelly bar. While the primary function of the reamer attachment 18 is tocut and loosen materials from the wall of the previously drilled openingso such loosened materials will fall to the bottom of the opening, ithas been found that a considerable quantity of removed materials canaccumulate above the bottom deck 52 of the reamer 18. These materialscan be hoisted out of the hole and thrown off the reamer by the rotationthereof. Ordinarily the loosened materials which accumulate in thebottom of the hole 12 will be subsequently removed therefrom through useof an auger flight 16 or a bucket auger whenever such accumulatedmaterials block the further downward progress of the reaming operations.

When the enlarged hole 22 has been completed to the full desired depth,the derived hole may be used for numerous purposes. In many instances itis desirable, however, to provide an even further enlarged opening inspaced positions along the vertical extent of the hole. In theconstruction of missile silos as well as in the construction of buildingfootings, improved structural or foundation characteristics may beexpected through provision of a bell footing at the bottom of thedrilled and reamed hole. Such enlarged bell at the bottom of the holecan, of course, provide an increased area of contact for thedistribution of the load carried by a structural member formed in thedrilled hole. Similarly, it is often desirable to provide an enlargedcross-section or collar ad acent the top of the drilled hole or at someother location along the vertical extent thereof.

In the construction of the described missile silo a lower bell footingand an upper collar have been desired. FIG- URES 1 and 2 show anddisclose a type of under-reamer 23 that has been found useful in thedigging of such bell footing and collar structures. Here an under-reamer23 1s preferably built with a cross-shaped frame structure made up ofradially disposed arms 61 joined to the kelly bar socket 62 andextending at ninety degree positions therefrom. The outer ends of thearms 61 provide support for a segmental guide surface 63, which ispreferably of size corresponding to the diameter of the finished andreamed hole 22. A top plate 64 interconnects such guide surface 63 andthe top of the cross bars 61. In addition to providing brace support forthe guide surface 63, the top plate 64 cooperatively with an arm 66provides support for a pivot pin 67. A cutter arm 27 is adapted forpivoting movement about such pin 67. A plurality of holes 69 areprovided through the top surface of the plate 64. Cutter arm 27 is ofsuch length that it will extend beyond the guide face 63 when the cutteris disposed in aligned radial position with respect to the arms 61. Atother angular positions about the pivot 67 the cutter arm 27 will extenda different distance past the guide surface 63 or may be retractedinwardly therefrom. Such changes in the extension of the cutter arm 27may be made by the placement of a pin 71 in a selected hole 69. If thepin 71 is placed in a hole such as that illustrated, the cutter arm 27will be backed up against the pin when the under-reamer is rotated inthe direction shown by the arrow. Since the cutter arm 27 is free tomove pivotally except as such movement is blocked or limited by the pin71, reverse rotation of the under-reamer 23 will be accompanied by theretraction of the cutter arm so that the entire assembly may be removedthrough the previously reamed hole.

As in the prior instance, the top plate 64 and the plates 72 disposedabove cross braces 70 provide convenient walkways for personnel. In theoperation of the underreamer for digging a bell extension at the bottomof a drilled and reamed hole 22, the cutter arms 27 will be retracted toa position radially inside of the guide surfaces 63. The entireunder-reamer 23 will then be lowered by extension of the kelly bar tothe bottom of the hole. Attendant personnel can then place the stop pins71 in corresponding holes 69, and subsequently rotation of theunder-reamer 23 will gradually bring the cutter bars 27 up against suchstop pins 71. To maintain balance the diametrically opposed bars 27should be extended the same distance while bars and cutters on theadjacent following assemblies may be at different radial positions toprovide a progressive cut. The outward movement of the cutter bars 27results from an interaction between the earth structure and the cutterbits 73 on the cutter bars 27. When all of the cutter bars have come toan extended position against their respective pins 71, the pins can bereset successively until the full desired extension for the cutter bars27 has been obtained. After the cutter bars are fully extended, thekelly bar can be extended or retracted as it is rotated so that theteeth 73 will cut and remove earth to provide the desired bellstructure. When the full out has been completed, reverse rotation willfree the cutter bars by moving them to a retracted position so theunder-reamer may be removed through the previously reamed hole 22. Sincethis operation in effect undercuts the earth structure, the efiiciencyof dirt removal is quite good. It has been found, however, that it isagain advisable to have the cutter bits disposed in non-followingpositions so that each bit cuts a separate and distinct path. Aspreviously mentioned, the desired non-following pattern may be obtainedby different placement of the pins 71 on adjacent assemblies or bychanging the cutter bit placement pattern on separate cutter bars 27.

While separate embodiments of the invention have been shown anddescribed, it should be apparent that the invention is susceptible tovarious modifications and changes. All such modifications and changes ascome within the scope of the present claims are deemed to be a part ofthis invention.

I claim:

1. A reamer attachment for earth drilling apparatus adapted forenlarging the diameter of pilot holes or openings that have beenpreviously drilled to substantially the full torque capacity of thedrilling apparatus through use of conventional auger attachments carriedand rotated by the kelly bar of such earth drilling apparatus,comprising a vertically disposed kelly socket for the reception of thekelly bar of such earth drilling apparatus, a cross frame joined to saidkelly socket, guide members circumferentially disposed on the outerextremities of said cross frame and adapted to engage the walls of saidpreviously drilled pilot holes or openings, cutter bits disposedadjacent said guide members in non-following position each with respectto the cutter bit circumferentially next adjacent thereto for slightlyenlarging the bore diameter of said pilot hole and to provide a guidebore in said earth structure, extension arms extending radiallyoutwardly past said first cutter bits at circumferentially spacedpositions, and cutters on said extension arms disposed for cutting andreaming an opening of substantially increased diameter, said cuttersbeing likewise disposed in non-following position each with respect tothe cutters circumferentially next adjacent thereto whereby each of saidcutter bits and cutters will engage, cut and remove a portion of earthwall to progressively ream and enlarge said original pilot opening andguide bore.

2. A reamer attachment for earth drilling apparatus adapted forenlarging the diameter of pilot holes or openings that have beenpreviously drilled to substantially the full torque capacity of thedrilling apparatus through use of conventional auger attachments carriedand rotated by the kelly bar of such earth drilling apparatus,comprising a vertically disposed kelly socket for the reception of thekelly bar of such earth drilling apparatus, a cross frame joined to saidkelly socket, guide members circumferentially disposed on the outerextremities of said cross frame and adapted to engage the walls of saidpreviously drilled pilot holes or openings, cutter bits disposedadjacent said guide members in non-following posi tion each with respectto the cutter bit circumferentially next adjacent thereto for slightlyenlarging the bore diameter of said pilot hole and to provide a guidebore in said earth structure, intermediate extension arms extendingradially outwardly past said first cutter bits at circumferentiallyspaced positions, cutters on said intermediate extension arms disposedfor cutting and reaming an opening of substantially increased diameter,upper extension arms extending radially outwardly past thecircumferential limits of said intermediate extension arms, and cutterson said upper extension disposed for cutting and reaming an opening ofdiameter greater than that cut by said intermediate extension, saidcutters being likewise disposed in non-following position each withrespect to the cutter circumferentially next adjacent thereto wherebyeach of said cutter bits and cutters will engage, cut and remove aportion of earth wall to progressively ream and enlarge said originalpilot opening and guide bore.

3. A reamer attachment for earth drilling apparatus adapted forenlarging the diameter of pilot holes or openings that have beenpreviously drilled to substantially the full torque capacity of thedrilling apparatus through use of conventional auger attachments carriedand rotated by the kelly bar of such earth drilling apparatus,comprising a vertically disposed kelly socket for the reception of thekelly bar of such earth drilling apparatus, a cross frame joined to saidkelly socket, guide members circumferentially disposed on the outerextremities of said cross frame and adapted to engage the walls of saidpreviously drilled pilot holes or openings, cutter bits disposedadjacent said guide members in non-following position each with respectto the cutter bit circumferentially next adjacent thereto for slightlyenlarging the bore diameter of said pilot hole and to provide a guidebore in said earth structure, diametrically opposed intermediateextension arms extending radially outwardly past said first cutter bits,diametrically opposed upper extension arms extending radially outwardpast said intermediate extension arms at circumferential positions awayfrom said intermediate extension arrns, and cutters on said extensionarms disposed for cutting and reaming openings of successively increaseddiameter, all of said cutters being likewise disposed in non-followingposition each with respect to the cutters circumferentially nextadjacent thereto whereby each of said cutters and cutter bits willengage, cut and remove a portion of earth wal' to progressively ream andenlarge said original pilot opening and guide bore.

4. A reamer attachment for earth drilling apparatus adapted forenlarging the diameter of pilot holes or openings that have beenpreviously drilled to substantially the full torque capacity of thedrilling apparatus through use of conventional auger attachments carriedand rotated by the kelly bar of such earth drilling apparatus,comprising a vertically disposed kelly socket for the reception of thekelly bar of such earth drilling apparatus, a cross frame joined to saidkelly socket, guide members circumferentially disposed on the outerextremities of said cross frame and adapted to engage the walls of saidpreviously drilled pilot holes or openings, cutter bits disposedadjacent said guide members in non-following position each with respectto the cutter bit circumferentially next adjacent thereto for slightlyenlarging the bore diameter of said pilot hole and to provide a guidebore in said earth structure, diametrically opposed intermediateextension arms extending radially outwardly past said first cutter bits,diametrically opposed upper extension arms extending radially outwardpast said intermediate extension arms at circumferential positions awayfrom said intermediate extension arms, cutters on said extension armsdisposed for cutting and reaming openings of successively increaseddiameter, all of said cutters being likewise disposed in non-followingposition each with respect to the cutters circumferentially nextadjacent thereto whereby each of said cutters and cutter bits willengage, cut and remove a portion of earth wall to progressively ream andenlarge said original pilot opening and guide bore, and said cutters onsaid intermediate and upper extension arms being of proper number andradial position to balance the torque forces of the diametricallyopposed and circumferentially following positions.

References Cited by the Examiner UNITED STATES PATENTS 883,137 3/1908Karns 17'5-384 892,849 7/1908 Karns 175-384 X 1,172,065 2/1916 Slettenet al. 175-391 X 1,436,890 11/1922 Mathews 175-263 X 1,667,155 3/1927Higdon 175263 2,684,834 7/1954 Miller et al. 175-53 2,843,362 7/1958Degen 175385 X 2,960,312 11/1960 Kandle 175391 X 3,011,567 12/1961Turner 175--53 3,077,235 2/1963 Govin 175391 X CHARLES E. OCONNELL,Primary Examiner.

JACOB L. NACKENOFF, Examiner.

R. E. FAVREAU, Assistant Examiner.

1. A REAMER ATTACHMENT FOR EARTH DRILLING APPARATUS ADAPTED FORENLARGING THE DIAMETER OF PILOT HOLES OR OPENINGS THAT HAVE BEENPREVIOUSLY DRILLED TO SUBSTANTIALLY THE FULL TORQUE CAPACITY OF THEDRILLING APPARATUS THROUGH USE OF CONVENTIONAL AUGER ATTACHMENTS CARRIEDAND ROTATED BY THE KELLY BAR OF SUCH EARTH DRILLING APPARATUS,COMPRISING A VERTICALLY DISPOSED KELLY SOCKET FOR THE RECEPTION OF THEKELLY BAR OF SUCH EARTH DRILLING APPARATUS, A CROSS FRAME JOINED TO SAIDKELLY SOCKET, GUIDE MEMBERS CIRCUMFERENTIALLY DISPOSED ON THE OUTEREXTREMITIES OF SAID CROSS FRAME AND ADAPTED TO ENGAGE THE WALLS OF SAIDPREVIOUSLY DRILLED PILOT HOLES OR OPENINGS, CUTTER BITS DISPOSEDADJACENT SAID GUIDE MEMBERS IN NON-FOLLOWING POSITION EACH WITH RESPECTTO THE CUTTER BIT CIRCUMFERENTIALLY NEXT ADJACENT THERETO FOR SLIGHTLYENLARGING THE BORE DIAMETER OF SAID PILOT HOLE AND TO PROVIDE A GUIDEBORE IN SAID EARTH STRUCTURE, EXTENSION ARMS EXTENDING RADIALLYOUTWARDLY PAST SAID FIRST CUTTER BITS AT CIRCUMFERENTIALLY SPACEDPOSITIONS, AND CUTTERS ON SAID EXTENSION ARMS DISPOSED FOR CUTTING ANDREAMING AN OPENING OF SUBSTANTIALLY INCREASED DIAMETER, SAID CUTTERSBEING LIKEWISE DISPOSED IN NON-FOLLOWING POSITION EACH WITH RESPECT TOTHE CUTTERS CIRCUMFERENTIALLY NEXT ADJACENT THERETO WHEREBY EACH OF SAIDCUTTER BITS AND CUTTERS WILL ENGAGE, CUT AND REMOVE A PORTION OF EARTHWALL TO PROGRESSIVELY REAM AND ENLARGE SAID ORIGINAL PILOT OPENING ANDGUIDE BORE.